Superconducting Magnet R&D for Accelerators

B. Auchmann CERN/PSI, J. Gao, R. Felder, G. Montenero, S. Sanfilippo, S. Sidorov PSI L. Brouwer, S. Caspi LBNL Superconducting Magnet R&D for Accelerators SPS Annual Meeting, 29.8.2018 Work supported by the Swiss State Secretariat for Education, Research and Innovation SERI.

Overview • Motivation • Nb3Sn Technology Challenges • US, China, and CERN magnet programs • FCC-Design-Study magnet R&D • EuroCirCol • CHART – PSI/ETHZ/UniGE/EPFL • Next steps

FCC Design Study European Strategy for Particle Physics 2013: “... to propose an ambitious post-LHC accelerator project ..., CERN should undertake design studies for accelerator projects in a global context, ... with emphasis on proton-proton …high-energy frontier machines ... coupled to a vigorous accelerator R&D programme, including high-field magnets and high-gradient accelerating structures, ...” • International FCC collaboration (CERN as host lab) to study: • pp-collider (FCC-hh)  main emphasis, defining infrastructure requirements • ~100 km tunnel infrastructure in Geneva area, site specific • e+e- collider (FCC-ee), as potential first step • p-e (FCC-he) option, integration one IP, e from ERL • HE-LHC with FCC-hhtechnology • CDR for end 2018 ~16 T  100 TeVpp in 100 km [M. Benedikt, fccw2017]

CEPC / SPPC AsiaHEP/ACFA 2016: “… The past few years have seen a growing interest in a large radius circular accelerator ... ultimately for proton-proton collisions at the high-energy frontier. We encourage the effort lead by China in this direction, and look forward to ... the technical design ...” 75 TeVCoM 12-T magnets ACFA .. Asia Committee for Future Accelerators AsiaHEP .. Asia-Pacific High Energy Physics Panel • [Q. Xu., fccw2017]

Nb3Sn Superconductor • The only technically mature and affordable superconductor for 9-16 T magnets. LHC FCC-hh

SC Dipoles for Accelerators Racetrack test coils without beam aperture. Racetrack Block coil 3 Cos D10 BNL (Sampson) [1] G. de Rijk Still a long and long road ahead for 14.3-m-long 16-T dipole. (Longest Nb3Sn magnet to date: LARP LQ quad with 3.7 m.)

Strain-Sensitivity of Nb3Sn Wires • Reversible and irreversible degradation of impregnated Nb3Sn wires under transverse pressure. • Epoxy impregnation helps to distribute the mechanical load. [C. Senatore et al.]

Mechanics Challenge Courtesy S. Farinon, INFN Example: Cos-theta option of 16-T FCC dipole. • Keep coils under compression at all stagesof operation  avoid stick-slip motion. • Forces scale quadratically with field. • For 16 T, dipole forces of 1.5 kt/m pull coil apart. • 10 µm abrupt movement is enough to cause quench. • Minimize stress on stress-sensitive Nb3Sn. • Limit is of the order of 150 to 200 MPa.

Mechanics Challenge 135 MPa @ 16 T Courtesy: C. Senatore • Canted Cosine Theta design advocated by LBNL (US). • Individual support of turns promises a decisive reduction of coil transverse stress. • Many challenges ahead: • former advanced manufacturing • impregnation scheme and training performance • quench protection

US MDP Magnet R&D Program • LBNL (Lawrence Berkeley Nat. Lab.) : • CCT technology development • with ultimate goal to build hybridHTS/LTS magnet towards 20 T • FNAL (Fermi National Lab.): • 15-T cos-theta magnetin innovative mechanical structureto be tested 2018, • followed by 16-T magnet possiblywith CCT-like stress management. [S. Caspi and A. Zlobin, usmdp2018]

SPPC Magnet Plans [Q. Xu, fccw2017] • SPPC design featuring • iron-based superconductor. • cost-saving 12-T magnets (75 TeV) • common-coil design • Practical R&D for the next years is focused on building flat Nb3Sn racetrack coils. • (IHEP contributes Nb-Ti CCT magnets to HL-LHC, too.)

CERN 16-T R&D Program [D. Tommasini, usmdp2018] [J. van Nugteren, mt25 conf. 2018] • Main project for now: HL-LHC • High-field Nb3Sn racetrack coilsas testbeds and demonstrators for • conductor and cable in 16-18 T field • mechanical structure • mechanical conductor limits • internal splices, etc. • First test in 2018. • HTS insert program had first test in 2017. • Thermal stability proven: no quenches! • Conductor price as the only obstacle.

EuroCirCol WP5 Block coil Canted Cosine Theta Cos-theta Common coils European Circular Energy-Frontier Collider Study (started 2015) Magnets fulfill specs for both,FCC-hh and HE-LHC. • [D. Tommasini, http://cern.ch/fcc/eurocircol]

CHART Accelerator Research Network – Magnet Activities ETHZ EPFL UniGE

CHART-PSI Goals towards FCC Requirements Ribs Spar CD1 CD2 Joint funding from CHART and the FCC design study from mid 2016 until the end of 2019. Goal:Demonstrate key technological features of an efficient 16-T CCT in two-layer technology model magnets. Thin and ribs spars Exterior mechanical structure Fast quench detection and CLIQ protection. Wide Rutherford cable. Inclined channels. Improved impregnation procedures.

CHART-PSI Status Overview • Within 14 months CHART-PSI has, among others: • Built and commissioned a lab from scratch. • Designed and procured all magnet components and tooling. • Launched epoxy-resin R&D with ETHZ. • Passed successfully a Production Readiness Review on Aug. 28. • Next year we will finalize the construction of the CD1 magnet, test it, and construct a second set of coils called CD2. • For more info on the CHART-PSI magnet program see talks by Giuseppe Montenero and Jiani Gao.

Next Steps for FCC R&D at CHART-PSI Magnets Long models 2023-27 Prototypes 2026-31 Pre Series 2031-35 Series production 2035-41 (1200 magnets/y) Short models 2018-23 Euro-CirCol Design [M. Benedikt, fccw2017] • FCC design study recommends to build all four 16-T magnet types until 2023/24. • CHART-PSI would build the 4-layer CCT, in collaboration with LBNL and CERN. • Additional infrastructure required for mounting of yokes / shell welding. • Focus on industrialization of manufacturing and further cost reduction. • Advanced-manufacturing initiative for winding formers.

Conclusion • High-field magnet R&D towards FCC-hh/HE-LHC specs is gaining momentum. • Agreements under preparation or already signed with four European institutes to build 16-T magnets until 2023/24. • The effort is more heterogeneous and dynamic than it has been for 20 years. • US programs are increasingly contributing to FCC R&D. • CHART is coordinating regularly with LBNL our R&D on the CCT concept. • HTS conductors are used successfully in small-scale R&D and would be most desirable if the price were lower. Will first appear in form of inserts in LTS outserts. • CHART is establishing itself as actor in accelerator-magnet R&D. • Many more opportunities ahead for collaboration under the CHART/FCC umbrella.

Main References • http://cern.ch/fcc • http://cern.ch/fccw2015 • http://cern.ch/fccw2016 • http://cern.ch/fccw2017 • http://cern.ch/fccw2018 • US-MDP collaboration meeting (link protected). • MT-25: http://mt-25.org

Nb3Sn Cable Wärmebehandlung Subelementmit A15 Phase The superconducting A15 phase is brittle and strain sensitive.Niobium and Tin are, therefore, co-extruded in the Rod-Restack Process into a strand. In wind-and-react processes, several 10s of strands form a Rutherford cable, that is insulated and usedto wind a coil. The A15 phase is created during a heat treatment of 180 h at up to 660ºC. Pictures from C. Sanabria PhD Thesis, FSU

Superconducting Accelerator Magnet Technologies Block Coil Cosine Theta Coil High efficiency. On paper, simpler end design. Peak stress in low-field region. High efficiency. Difficult stress management and coil end design. Canted Cosine Theta (CCT) Common Coil Simple manufacturing, low coil stress.Reduced efficiency. Simple coil ends.Higher stored energy.Involved mechanics.Slightly lower efficiency. 26 [Courtesy of L. Brouwer, S. Caspi, [2] M. Duharte, S. Farinon, C. Lorin, J. Munilla, M. Sorbi, F. Toral, Q. Xu]

US MDP HTS Program at LBNL [S. Prestemon, usmdp2018] • Bi2212 has made dramatic strides in Jc over last 3 years • Wire has been cabled and tested in racetrack configuration. • 50-bar heat treatment at 900ºC (FSU) is a technical challenge. • Stress sensitivity are to be addressed for high-field applications. • Roadmap being developed to integrate Bi2212 CCT in a high-field hybrid magnet design • REBCO CORC is used to build CCT coils. • Further reduction in diameter will permit to make cable from CORC wire with high Je. • Advances have been made on splicing and quench detection. • REBCO and CORC prices are still prohibitively high for a more vigorous magnet R&D.

CHART Magnet Design of CCT Type Ribs Spar • Increase Je • First CCT design fulfilling all EuroCirCol criteria • Conductor needed for FCC-hh: 9.77 kti.e., +30% wrt. cosine theta • Total inductance: 19.2 mH/m • Total energy: 3.2 MJ/m • Keys to an efficient CCT design: • Thin spars • Wide cable, large strands • Thin ribs • Efficient protection (less copper)

Superconducting Magnet R&D for Accelerators